Fluid coking



Sept. 14, 1965 R. L. scHx-:UERMANN ETAL 3,206,392

FLUID COKING' Filed Deo. 11. 1961 Roberr L. Scheuermclnn g I Richard L. Carr 'mentors Enf/@7l Poent Attorney United States Patent O 3,206,392 FLUID COKING Robert L. Scheuermanm Florham Park, NJ., and Richard L. Carr, Emlenton, Pa., assignors to Esso Research and Engineering Company, a corporation of Delaware Filed Dec. 11, 1961, Ser. No. '158,239 6 Claims. (Cl. 208-127) This invention relates to thermal cracking and iuid coking and more particularly relates to a process and apparatus for controlling the particle size of the coke particles in the unit.

In il'ui-d coking the coke particles as a fluidized bed in the rea-ctor are contacted with oil feed and the oil feed cracked. When the oil feed is cracked, one of the products is coke which is deposited on the coke particles and as a result the coke particles grow or increase in size and if this is allowed to continue the coke particles become too large to 'be properly -uidized and the fluid bed may become deiiuidized.

Coarser particles lof coke are withdrawn as product coke from the coldng unit and hence it is necessary to s-upply smaller or iiner coke particles as seed coke to the coking unit. It is also desirable to remove fines or extremely small coke particles from the coarse coke product being withdrawn from the process.

in some of the prior art patents, water has been used to quench the coarse coke product to be withdrawn and this quenching forms steam which is used to elutriate fines from the coarse coke product. In lsome fluid coking plants, this has not been entirely satisfactory and the poor elutriator vessel performance is probably due to slugs or large batches of coke dumped into thc elutriator vessel which causes an immediate rise in elutriator solids bed temperature. Since the quench water is under elutriator solids bed temperature control, the quench water control valve opens up and injects ia large amount of water into the quenching zone. The periodic slugs of hot coke and quench water .tend to cause poor control of elutriation. Since good elutriation depends on steady operation, separation of iines from the product coke is yusually poor.

According to the present invention, `a quench-elutriator vessel is provided which gives controlled separation of iine and coarse coke particles by maintaining separate elutriation and quench zones. More specifically, the elutriator vessel is provided with a separate central ver- :tical internal elutriation tube in which elutriation with steam is carried out. Hot coke particles from the burner vessel are introduced into the upper portion of the elutriation tube and pass down countercurrent to steam introduced into the lower portion of the elutriation tube for upward passage therethrough. The velocity of the steam is controlled by an external hand control valve and flow meter.

Coarse coke particles flow out of the bottom of the elutriation tube into a dense fluid bed quenching Zone of coke particles in the bottom of the vessel surrounding the elutriation tube. Quench water is introduced into `the bottom dense fluid bed of coke particles forming an -annulus arou'nd the elutriation tube so that the water is flashed to steam and the steam formed is passed upwardly around and not up through lthe elutriati-on tube. The elutriated coke nes and steam leave the open end at -the top of the elutriation tube and steam leaves the dense uid bed of coke surrounding the elutriation tube and leave the top of the elutriator vessel for return to the burner in the coking unit. In this way iines are returned to the coking unit and this assists in maintaing the proper proportion of fines in the circulating coke solids to provide good fluidity of the bed in the reactor and burner.

ICC

Attrition of the coke particles to provide iines is also usually required. Coarse coke particles as product are withdrawn from the dense bed of coke particles in the bottom of the elutriator vessel.

With the present invention, better coke particle size control is obtained by maintaining separate zones for the elutriation and quenching of the hot coke. In addition, there are less Ifines in the coarse product coke withdrawn from the ook-ing unit and this is the preferred product. As pointed out above the present invention also provides a high proportion of iines in the circulating coke and this provides smoother coke circulation and better fluid beds in the coker reactor and burner. More fines are retained in the system and this lwill allow lower .attrition steam requirements.

The fluid ook-ing process is a well known process and is described in Pfeiffer et al. Patent No. 2,881,130, granted April 7, 1959, and the disclosure of this patent is incorporated herein by reference thereto,

In the drawing:

FIG. 1 represents a dia-grammatical showing of the entire process; and

FIG. 2 represents a vertical cross-sectional View of one form of an enlarged quench-elutriator vessel of the present invention.

Referring now to the drawing, the reference character 10 designates a coking vessel land reference character 1-2 designates a burner vessel. Liquid hydrocarbon feed is introduced or sprayed into coking vessel 10 through line 14. Liquid feeds suitable for the present invention are heavy or reduced crude petroleum oils or vacuum bottoms or residual hydrocarbon oil which cannot be vaporized without decomposition. Such oil feeds may have an API gravity between about 10 and 20, and a C-onradson carbon between about 5 `and 50 wt. percent. The oil feed can be preheated by conventional means, not shown, or by exchange with the reactor vapor products discharged from line 15 to between about 400 and 800 F. and is introduced into the dense uidized turbulent coke bed 16 in the coking vessel 10. Preferably the oil feed is introduced into the fludized bed 16 at a multiplicity of points. The highly turbulent nature of the uidized bed 16 also assists in causing rapid dispersion -of the oil feed throughout the bed 16.

Preferably the oil feed 'is mixed with between about 0.25 and 0.50 wt. percent steam on the oil feed to assist in dispersing the oil feed in the bed 16. The steam is introduced through line 17. The coking vessel 10 contains coke particles ranging in size between about 40 `and 5000 microns with most of the particles being between yabout and 2500 microns. Steam 4is also introduced through line 18 into the bottom porti-on of the fluid bed of coke 16 to function as a stripping gas to remove or displace hydrocarbon vapors from the coke. Stripping gas velocity is between about 0.3 and 5.0 ft./ sec. The stripping gas may be injected into the dense iiuid coke bed through nozzles at high velocity to cause attrition or grin-ding of the larger coke particles to maintain the desired coke particle size. To be effective as an attrition gas, the steam is introduced .at supersonic velocities.

The coke particles within the bed 16 are maintained in a turbulent fluidized condition by the gases and vapors passing upwardly therethrough. The gases and vapors include 'the iiuidizing and stripping gas and the vapors and gases formed by coking or cracking of the oil feed. The fluidized bed 16 has a level indicated at 19 superimposed by a dilute phase `20. The average superficial velocity of the npowing gaseous material is between about 0.5 and 5.0 ft./sec. depending on the size of the coke particles making up the bed 16. The density `of the fluid bed 16 may be between 30 and 50 lbs/cu. ft. The temperature in f the lower :por-tion of burner vessel 12.

the bed 16 and vessel 10 is maintained between about 850 F. and 1200 Higher temperatures up to about 1800 F. may be used in processes for cracking the oil feed to -olens, diolelins, aromatics, etc., and coke.

The pressure in coking vessel may be between about 1 and 100 p.s.i.g. iThe hydrocarbon oil Ifee-d rate may be between about 011 and 3.0 weight of oil .per hour per weight of solids (w./hr./w.) present in the iluid bed 16.

i In the fluid bed 16, the toil feed is cracked or converted to hydrocarbon vapors and coke. The -vaporous hydrocarbons are lower boiling hydrocarbons and these hydrocarbons leaving the bed 16 `and passing into the dilute phase 20 carry entrained solids. In the dilute phase 20, there is some settling of solids.

The vapors and gases lpassing up through dilute .phase 20 `are passed into gas-solids separating means 20 such as one or more cyclone separators in series arranged inside an-d at the top of coking vessel 10 for separating entrained solids from vapors and gases which pass out overhead through line 15. The separated solids `are returned to or above the dense fluidized bed 16 through -dip -leg 26.

The vapors and gases passing overhead through line are further treated las desired and may be fractionated to separate :gasoline from higher boiling hydrocarbons and gas and the higher boiling hydrocarbons may be recycled to :the coking vessel or removed from the system as product. They may ,also be used to -preheat the oil feed to the reactor.

To supply heat for t-he ooking ves-sel 10, coke particles are circulated from vessel 10 to external burner vessel 12 where partial combustion of the coke particles occurs and the coke particles are heated to a higher temperature. Coke particles are withdrawn from the bottom po-rtion of the coking vessel 10 through standpipe 30 having a control valve 32 iat its lower end and suspended in a lluidizing -gas introduced through line 34 'below valve 32 and the resulting suspension is passed through line 36 into The burner vessel is preferably a two phase burner where the coking particles settle out to yform a dense fluidized turbulent bed 38 having a level indicated at 40 superimposed by a dilute phase 42. In the burner vessel 12, a portion of the coke is consumed by burning and the remainder of the coke particles are heated to a temperature between about 50 F. and 300 F. higher than the temperature in coking vessel 10, that is, between about 1050J F. and 1250 F. Other types of burners such as a high velocity transfer line burner or the like may 'be used instead of the fluid bed burner.

The combustion gas passes up into dilute phase 42 and there is some separation and settling of the entrained coke solids. The combustion gas then passes into gas solids separation means 46 such as one or more cyclone separating mean-s located inside and `at the top of burner vessel 12 to separate entrained solids which -are usually returned to above the -dense .iluidized bed 38 through `dip leg 48. Hot combustion gas passes overhead through line S0 and may be passed through a waste heat boiler or other heat exchanger means to recover heat from the combustion gas before venting it to the atmosphere. Air is introduced into the bottom portion of burner vessel 12 through line 51.

The gases passing up through burner vessel 12 main- 4tain the coke particles in a dense turbulent uidized condition. The gases pass up through the bed 38 at an average superfici-al velocity between about 0:5 and 5.0 ft./sec. an-d the density of the iiuid bed 38 is between about 30 and 50 lbs./ cu. ft. The hot coke particles are withdrawn trom dense fluidized bed 30 in burner vessel 12 through standpipe 52 having a control valve 53 and steam kor the like is introduced below the valve 53 through line 54 and the suspension passed through `line 55 and recycled to the upper portion of `coking vessel 10. y

Another portion of the heated coke particles 1s withdrawn from burner vessel 12 and from a well formed by vertically extending partition 56 which extends up from the bottom yof burner vessel 12. The coke .particles ow down from the well into standpipe 57 extending downwardly from the well and provided wi-th control valve 58. Gas such as steam or the like is introduced into the withdrawn coke particles below v-alve '58 to form a dilute suspension which is passed through -line 63 into the vertically arranged quench elutriator vessel 64 `diagrammatically shown in FIG. l and in greater detail in FIG. 2 yor the solids may lflow down through standpipe 57 and control valve and be .introduced as such as a dense fluidized s-trearn without further introduction of .suspending gas through line 63 into quench elutriator vessel 64. Quench water is introduced through line 72 into the lower portion 4of elutriator vessel 64 and large cooled coke particles are withdrawn from the bottom portion lof vessel 64 through line 66. A gaseous suspension containing fines or finely divided elutriated coke particles is passed `overhead through line 70 and returned to burner vessel 12 along with the steam formed from the quench water.

Referring now to FIG. 2, the quench-elutriator vessel is sh-own in greater detail. .The vessel 64 has an inverted conical bottom 74 but the shape is not critical and a rounded bottom =or other forms may be used. The vessel 64 is cylindrical and has a substantially uniformv diameter for substantially its entire length. The vessel has a rounded top ending in outlet line 70 heretofore referred to. A iluidized bed of coke solids 78 having a level indicated at 79 i-s collected in the lower portion of vessel 64 .as wil-1 be presently described. Solid-s outlet line 66 extends up into vessel 64 above the lower end of tube 80 and maintains the iluidized bed 78 in vessel 64.

The vessel 64 is provided with a vertically arrange internal open-ended hollow elutriation tube or pipe 80 which is coaxial with the vessel 64 and has its lower end $2 spaced above `and from bottom portion 74 of the vessel 64 and has its upper end 36 spaced from t-he top -of vessel `64 as at 88 so that the tube 80 is entirely within ythe vessel 64. The tube 80 is shown as bein-g cylindrical and of uniform diameter, but the diameter need not be uniform and other shapes of tube 80 :may be used. The tube or pipe 80 is supported and held rigid in vessel 64 in any conventional manner such .as by horizontal arms or supports 92 which are preferably secured at one end to the inner wall of the upper portion 75 of vessel 64 and -at the other end to t-he outside wall of the tube 80. The elutriation tube 80 is provided to elutriate and separate nes from the coke particles and to return the separated tines to the 'burner vessel 12. A steam line 102 is provided which is shown as extending through the bottom portion 74 of vessel 64 and into the lower portion of elutriation tube 80. The outlet er1-d 104 of Iline 102 is preferably provided with a plurality branch distributor each having a perforated cap outlet. The steam is at a temperature between aboutf300" F. and 1000 F.

The inner open end of steam line 102 terminates at 104 `above the lower end Iof elutriation tube 80 and centrally thereof to direct steam upwardly in the tube 80. Coke particles to be elutriated are withdrawn from the burner vessel 12 through line 63 and introduced into the upper end of the tube 80 by the downwardly directed open end 105 of pipe or line 63. Directly beneath the outlet end 105 -of the .pipe 63 in the tube 80 is a Idisc 106 and donut construction 107 for distributing the coke particles from pipe 63 uniformly over the crossdsectional area of the elutriator tube 80.

Steam pipe or line 102 has an external control valve 107 which can be used manually or automatically to control the velocity of the steam for elutriation being introduced through line 102. The superficial velocity of the steam in elutriator tube 80 should be between about 3 and 30 ft./sec. The exact quantity of steam to be added through line 102 will depend on the desired cut point` of the coke particles size, the size distribution of the coke particles being introduced through line 63, the coke feed rate to the tube 80 and the required ratio of coke feed to net coke product to be withdrawn from the unit.

At high net coke production rates, the elutriation efciency falls off a small amount since it is dependent to some extent on coke loading and at such high rates, it is preferred to by-pass the elutriator tube 80 with some of the hot coke by passing it through by-pass valved line 110 provided as a branch line from line 63. By-pass line 110 conducts hot coke from the burner vessel 12 and line 63 directly into the quenching dense iluid bed 78 below the level indicated at 79. The open bottom end of line 110 is normally arranged below the level 79 of fluidized solids.

Fine coke particles are elutriated from the downflowing coke mixture in the elutriator tube S0 by the upowing steam from line 102 and the steam and entrained coke fines or line coke passes up through the top outlet end of tube 80 and into outlet line '70 for return to the dilute phase of the burner vessel 12 as shown in FIG. 1. Coarse coke particles ow out of the bottom of the elutriator tube 80 into the dense bed quenching zone 78 to be cooled by flashing water into steam.

Quench water or other liquid for cooling the coarse coke mixture introduced into the bottom portion or quench portion 78 of elutriator quench vessel 64 is introduced into the coke mixture through one or more lines 72 to quench and cool the coarse coke particles which are to be withdrawn as product through line or standpipe 66 and also to iluidize the coke particles in bed 78. The upper end of standpipe 66 determines the level 79 of dense bed 73 but the bed level could also be controlled by withdrawing coke from the bottom of the bed and controlling the withdrawal rate with a level controller and valve. The lluidized bed 78 also seals the bottom of tube 80 to prevent steam from entering the tube 80 from quench bed 78. Only enough quench liquid is introduced to be vaporized or flashed to steam so that the temperature of the quenched coke product is above the condensation point of Water and so that no water is present as such in the fluidized bed 78. Additional uidizing gas such as steam may be supplied through one or more lines 112 into the bottom 74 of elutriator vessel 64, if desired.

The Vaporized quench liquid as steam and some entrained coke lines leave dense fluidized coke bed 78 and pass up around and exterior to the elutriator tube 80 and through an annular passageway and leave vessel 64 through the passageway 88 between the top of tube 80 and the top of vessel 64 and join the elutriation steam and entrained lines from the top of tube 80 for return to the burner vessel 12 through line 70.

In the normal operation, hot coke particles will be passed through line 63 only and the downowing coke particles will be contacted countercurrently by steam rising from outlet 104 of steam line 102. At a given steam rate the free fall velocity of a certain diameter coke particle will be exceeded and a high percentage of coke particles smaller than thissize will be entrained overhead through line 70 and a high percentage of coke particles larger than this size will fall to the bottom of tube 80 and pass into the quench section or quench bed 78. The separation will not be perfect. A few large particles will go overhead and some small ones will go down. The fractionation depends on the loading. Water introduced through line 72 is flashed into steam and the steam is transported to the burner vessel 12 by overhead line 70 after passing through the annulus between the elutriator tube 80 and the quench vessel 64 and passageway 88 leading to line 70.

v The two principal variables affecting separation by elutriation are the elutriating gas velocity and the rate of feed coke particle mixture into the elutriator tube or column. In order to remove a major portion of the nes from the coarse coke, the elutriating gas velocity should be at least 1.5 to 3.0 times, that is, about twice the free fall velocity of the largest particle tube taken overhead. As the gas velocity is increased less of the coke fines fall to the bottom with the coarse material. If the gas velocity exceeds the free fall velocity of any particles of the coarse fraction, some of these coarse particles will be carried overhead and contaminate the fines.

F or practical purposes, the elutriating gas velocity may range from about 3 ft./sec. if it is desired to recover lines of about micron diameter and fines to about 30 ft./ sec. if the solids to be carried overhead are to include particles of about 1,000 micron diameter.

The solids feed rate to the elutriator tube also has a pronounced affect on the degree of separation of fines from coarse. For a given gas velocity, as the coke feed rate increases, the amount of lines going to the bottom increases. If there is any amount of coarse material going overhead because the gas velocity exceeds the free fall velocity of the fines actually desired, an increase in the solids or coke feed rate will decrease the amount of coarse material going overhead. At the same time, the total amount of material going overhead decreases in proportion to the amount dropping to the bottom. Consequently, there is an optimum ratio of solids feed rate to gas rate for each gas velocity which will give only a small amount of coarse material going overhead and only a small amount of lines going to the bottom.

For example to separate approximately 250 micron and smaller coke particles (free fall velocity about 4 ft./sec.) from coarser coke particles, the following Table I shows the best range of coke feed rate in pounds to steam rate in cubic feet at a given steam velocity in feet per second in order to get good separation of coke nes in elutriator tube 80.

T able I Rate of coke feed rate Gas velocity, ft./sec.: to gas rate lb./cu. ft.

In a specic example feeding about 30,000 barrels per day of residual petroleum oil having a gravity of about 8.2 A.P.I., an initial atmospheric boiling point of about 600 F. and a Conradson carbon of about 16.7 wt. percent are introduced into coking vessel 10 along with about 10 wt. percent steam on the fresh oil feed. The density of the lluid coke bed in vessel 10 is about 45 lbs./cu. ft. and the temperature of the coking uid bed in vessel 10 is about 970 F. The pressure in vessel 10 is high enough to overcome the pressure drop through the recovery equipment and is slightly above atmospheric pressure. Vaporous products pass overhead and are cooled, condensed and fractionated to separate lower boiling products as follows and coke formed:

In the following table, MM equals l million.

2.24 MM lbs/day 40 to 5,000 microns About 530,000 pounds of the gross coke per day are burned in burner vessel 16 to supply the heat required for t'he coking process or step in vessel 10. The temperature in the burner vessel i-s about 1150o F. The circulation rate of coke solids between the coking vessel 10 and burner vessel 12 is about 50 tons per minute.

The vessel 64 `in this example as shown in FIG. 2 is a straight sided one or a cylindrical one of a uniform diameter of about 8 feet and a total height of about 32 feet. The pipe 63 has an internal diameter of about l0 inches.

Coke, particle size range .has an internal diameter of about 6 inches and extends to level 104 -or the outlet end 104 slightly above the inlet lend of pipe 66. The top of tube 80 is spaced at 88 4from the top of vessel 64 a distance of about 1 foot. The disc 1,06 is about 1 foot in diameter andthe associated donut 107 has a ring section of-about 6 inches wide. The disc `10.6 is about 1 foot .below the -outlet I105 of line 63 and i the donut 107 is about 1 foot below :the disc 106. The

bottom 82 of `tube 80 is about 5 'feet above the lowest point of bottom 74 of vessel 64. The uppermost part of coarse coke product drawoff line 66 is at a 4slightly lower level than `the top or outlet 104 of steam line 102, that is, .about 7 feet above the lower end 82 of tube 80. About 247,500 pounds of vcoke per hour having a particle size `distribution .as follows:

Mesh, retained on: Wt. percent -on mesh at a temperature of about ll50 F. and a density of about 40 lbs/cu. ft. are introduced through line 63 into elutriator tube 80.

Steam at a temperature of about 350 F. and in an amount of about 14,000 lbs. per hour is introduced into the lower portion of elutriator tube 80 through line 102 to have a superficial velocity of about 7.9 ft./ sec. in tube 80. O1 the feed rate of steam can be given as 100 cubic feet per second. Under .these conditions the following separation is accomplished:

Stream lb./hr. of

Fine product Coarse product Coke mesh (Tyler) 177,000 70,500

The coke lines returned to vessel 12 in conjunction with attrition maintain the desired and selected proportion of to 150 micron fines of or above about 30 to 70 wt percent of the circulating coke mixture to maintain optimum fluidity of the coke mixture in the coking vessel, the burner Vessel, standpipesa etc.

About l.7 MM pounds per day of coarse coke particles at a temperature of about l000 F. are flowed down from the bottom of tube 80 into dense quenching bed 7 8.

About 120 cubic feet of dense uidized coke mixture having a density of about 40 lbs./cu. ft. at a uidizing velocity of about 2.0 ft./ sec. and a temperature of about 300 F. are retained in fluid bed '78 in the bottom of vessel 64.

About 0.22 lb. of water per pound of solid introduced into quenching Huid bed 78 is introduced into bed 78 through line 72 to cool the coarse coke particles in fluidized bed 78 to a temperature of about 300 F.

About 1.7 MM lbs. per day of coarse coke having7 a 8 particle size between about 40 and 5000 microns are withdrawn as coke product through line 66 andsent to storage.

By recovering coke fines and recycling them to thevnnit, the amount of attrition steam needed inthe stripping section 18`is reduced.

The vlevel of solids inthe bottom of the elutriator tube is -slightly higher than that yot the solids in bed 78 around tube v80.

The amountfof` steamfpassing through line -102 may be varied as desired by external valve 107 tochange elutriating conditions in tube S0 so that more or less coke fines may be 'separated or vlarger or smaller sizes than a selected size may be separated from the coke mixture. The steam control will also permit optimizing the elutriation conditions if-coke yfeed rate to the elutriator tube changes.

What is claimedis:

1. In a process wherein high boiling hydrocarbons are thermally cracked in a'fiuid coking process and coke particleslare circulated between a coking zone and a coke burning zone to partially burnthe coke particles tosupply heat lof cracking vand wherein -uid coking particles are withdrawn from said burning zone and wherein colte fines are separated from admixture with coarse coke .particles and the coke fines are returnedtosaid burning zone and coarse coke particles are withdrawn as `product coke, the irnprovement which comprises withdrawing a portion of the .coke mixture from said burning zone and :passing it to the upper portion of a vertically arranged central confined elutriating passageway surrounded by an annular chamber, said elutriating passageway and said annular chamber communicating at the bottom to form a quenching zone, introducing said mixture of coke fines and coarse coke particles into lthe upper portion of said central confined elutriating passageway, elutriating coke lines from said coke mixture by the countercurrent action of upflowing steam introduced as a separately controlled stream into the lower portion of Vsaid confined elongated elutriating passageway to separate coke fines overhead from coarse coke particles, passing the separated coarse coke particles into said quenching zone, injecting water into said coarse coke particles in said quenching zone to cool said coarse coke particlesand form steam which passes upwardly through said annular zone and which entrains coke iines from the coarse coke particles, combining the last mentioned steam containing entrained coke fines with the steam and coke iines leaving said `cen*- tral confined elongated elutriating lzone overhead and passing the combined stream to said burner zone and removing coarse coke particles as product coke from Said quenching zone.

2. In a process wherein high boiling hydrocarbons are thermally cracked in a uid coking process and coke particles are circulated between a coking zone and a coke burning zone to partially burn the coke particles to supply heat of cracking and coke particles are withdrawn as product coke, the improvement of recovering and returing coke fines from a portion of the withdrawn coke Imixture to said coking unit and withdrawing coarse coke product which comprises withdrawing a portion of the coke mixture from said burning zone and passing it to the upper portion of a vertically arranged elongated central confined passageway surrounded by an annular concentric zone, passing a separate stream of gas up through said central confined passageway for countercurrent treatment of said coke mixture to elutriate coke ines overhead from coarse coke particles, returning the elutriated fines and gas to said coking unit, passing the separated coarse coke particles to a bottom quenching zone concentric with said central conned passageway and communicating with said annular zone, introducing a vaporizable liquid into said quenching zone beyond the contines of said central conned passageway to ash the liquid into vapor to cool the coarse coke particles and to uidize said coarse coke particles, passing the formed vapor upwardly in said annular zone surrounding said confined central passageway but outside of said central passageway and withdrawing cooled coarse coke particles from said quenching zone as a coke product.

3. A process according to claim 2 in which the separate eiuents from said central confined passageway and the upper portion of said annular zone are combined and returned to said coking unit.

4. A11 apparatus of the character described including in combination a vertically arranged vessel having a top outlet and a bottom outlet, a vertically arranged hollow open-ended tube entirely within said vessel and having its upper end spaced from and discharging into said vessel top outlet, said tube having its lower end spaced from the bottom of said vessel, a pipe extending through the wall of said vessel and into the upper portion of said tube and opening downwardly for introducing solids downwardly in said tube, distributing means in said tube and directly below the outlet of said pipe, a second pipe extending through the wall of said vessel and into the lower portion of said tube, said second pipe having its outlet end opening upwardly for the introduction of upowing gas, said second pipe having a control valve exterior to said vessel, said vessel bottom outlet extending through the wall of said vessel and upwardly from the bottom thereof and above the bottom portion of said tube whereby solids passing from the bottom of said tube accumulate in the bottom portion of said vessel to seal the bottom of said tube, means for introducing a quenching liquid which is ashed on contact with the accumulated solids into the bottom portion of said vessel to lluidize accumulated solids therein, said bottom outlet being used to withdraw solids from said vessel.

5. An apparatus of the character described including in combination a vertically arranged vessel having a top outlet and a bottom outlet, a vertically arranged hollow open-ended tube entirely within said vessel and having its upper end spaced from and discharging into said vessel top outlet, said tube having its lower end spaced from the bottom of said vessel, a pipe extending through the wall of said vessel and into the upper portion of said tube and opening downwardly for introducing solids downwardly in said tube, a second pipe extending through the wall of said vessel and into the lower portion of said tube, said second pipe having its outlet end opening upwardly for the introduction of upowing gas, said second pipe having a control valve exterior to said vessel, said vessel bottom outlet extending through the wall of said vessel and upwardly from the bottom thereof and above the bottom portion of said tube whereby solids passing from the bottom of said tube accumulate in the bottom portion of said vessel to seal the bottom of said tube, means for introducing a uidizing medium into the bottom portion of said vessel to fluidize accumulated solids therein, said bottom outlet being used to withdraw solids from said vessel.

6. An apparatus according to claim 5 wherein-said tube is an elutriation tube, said solids are =hot fluid coke particles having a size range between about and 5000 microns and said iluidizing medium is a quenching liquid which is flashed on contact with the accumulated solids and said second pipe is used to separately introduce elutriation steam into said elutriator tube.

References Cited by the Examiner UNITED STATES PATENTS 2,779,719 1/57 Sptiz et al. 208--127 2,874,095 2/ 59 Boisture et al 208-127 2,885,272 5/59 Kmberlin 23-284 2,890,993 6/59 Kleiber 208-127 2,946,741 7/ 60 Miller 208-127 ALPHONSO D. SULLIVAN, Primary Examiner. 

1. IN A PROCESS WHEREIN HIGH BOILING HYDROCARBONS ARE THERMALLY CRACKED IN A FLUID COKING PROCESS AND COKE PARTICLES ARE CIRCULATED BETWEEN A COKING ZONE AND A COKE BURNING ZONE TO PARTIALLY BURN THE COKE PARTICLES TO SUPPLY HEAT DRAWN FROM SAID BURNING ZONE AND WHEREIN COKE FINES ARE SEPARATED FROM ADMIXTURE WITH COARSE COKE PARATICLES AND THE COKE FINES ARE RETURNEDTO SAID BURNING ZONE AND COARSE COKE PARATICLES ARE WITHDRAWN AS PRODUCT COKE, THE IMPROVEMENT WHICH COMPRISES WITHDRAWING A PORTION OF THE COKE MIXTURE FROM SAID BURNING ZONE AND PASSING IT TO THE UPPER PORTION OF A VERTICALLY ARRANGED CENTRAL CONFINED ELUTRIATING PASSAGEWAY SURROUNDED BY AN ANNULAR CHAMBER, SAID ELUTRIATING PASSAGEWAY AND SAID ANNULAR CHAMBER COMMUNICATING AT THE BOTTOM TO FORM A QUENCHING ZONE, INTRODUCING SAID MIXTURE OF COKE FINES AND COARSE COKE PARTICLES INTO THE UPPER PORTION OF SAID CENTRAL CONFINED ELUTRIATING PASSAGEWAY, ELUTRIATING COKE FINES FROM SAID COKE MIXTURE BY THE COUTERCURRENT ACTION OF UPFLOWING STEAM INTRODUCED AS A SEPARATELY CONTROLLED STREAM INTO THE LOWER PORTION OF SAID CONFINED ELONGATED ELUTRIATING PASSAGEWAY TO SEPARATE COKE FINES OVERHEAD FROM COARSE COKE PARTICLES, PASSING THE SEPARATED COARSE COKE PARTICLES INTO SAID QUENCHING ZONE, INJECTING WATER INTO SAID COARSE COKE PARTICLES AND FORM STEAM WHICH PASSES UPWARDLY THROUGH SAID ANNULAR ZONE AND WHICH ENTRAINS COKE FINES FROM THE COARSE COKE PARTICLES, COMBINING THE LAST MENTIONED STEAM CONTAINING ENTRAINED COKE FINES WITH THE STEAM AND COKE FINES LEAVING SAID CENTRAL CONFINED ELONGATED ELUTRIATING ZONE OVERHEAD AND PASSING THE COMBINED STREAM TO SAID BURNER ZONE AND REMOVING COARSE COKE PARTICLES AS PRODUCT COKE FROM SAID QUENCHING ZONE. 